The identity of the attackers was not immediately clear, but security sources said they were likely to be Islamist militants.

Meanwhile. the Egyptian army sent tanks across the Suez canal to Sinai, where Islamist gunmen kidnapped seven soldiers and policemen last week, state daily al-Ahram said on Monday.

Gunmen demanding the release of jailed Islamist militants seized the hostages on the road between the Sinai towns of el-Arish and Rafah on Thursday.

The kidnapping has drawn national attention to lawlessness in the strategic peninsula and enraged security forces in the area, who have blocked border crossings into Israel
and the Gaza Strip to pressure the government to help free their colleagues.

A video posted online on Sunday showed seven blindfolded men with their hands bound above their heads, who said they were the hostages, begging President Mohammed M0rsi to free political detainees in Sinai in exchange for their own release.

The video, which was the first sign of the hostages since their kidnapping, could not be independently verified. State newspaper Al-Ahram said security services were looking into its authenticity.

Morsi said on Sunday that "all options are open" to free the hostages. "We will not succumb to any blackmail," he wrote on Twitter shortly after the video was posted online.

Presidential spokesman Omar Amer told Egyptian state television that no talks were taking place with the kidnappers and that it would be unacceptable to negotiate with criminals.

The army shifted several units of troops to North Sinai "in preparation for taking part in a large-scale military operation to release the abducted soldiers if negotiations came to failure," the government said in a State Information Service statement in English on Sunday.